Device for Mitigating the Effects of Explosive Events

ABSTRACT

An explosive mitigation apparatus for use in mitigating the effect of an explosive event, the apparatus comprises blast detection means which is capable of detecting an approaching shock wave or electromagnetic wave, caused by the explosion of an explosive device or other ordnance and which produces an output signal indicative of an explosive event, a countermeasure device comprising a shaped explosive charge and a load in which the explosive charge, when detonated, causes the load to be ejected from the device as a high velocity jet at least partially in a direction towards the approaching fireball, blastwave(s) and/or fragments, and an initiator which causes the detonation of the countermeasure in response to the output signal from the blast detection means, the apparatus can be used to protect a vehicle or other object, or as a protective barrier around an explosive device that is being disarmed.

This invention relates to devices suitable for mitigating the deleterious effects—including blast wave (over-pressure and under-pressure), fireball and fragment damage ‘the effects’ of energetic events (such as, for example, the detonation of conventional munitions or improvised devices or other energetic events) ‘the explosive event’ on an object ‘the target’. It may also be employed to deflect, intercept or degrade the effects of projectiles of many types upon the target.

To date, various different solutions have been proposed for protecting targets from the effects of explosive events. Targets may be armoured to deflect, absorb or attenuate the effects. Taking the example of a vehicle-extra armour increases the weight and reduces the fuel economy of the vehicle. Shaping, such as the use of a v-shaped hull, increase the ride height and can have a detrimental effect on the stability of the vehicle. As such whilst effective these techniques do have significant drawbacks.

According to a first aspect the invention provides explosive mitigation apparatus for use in mitigating the effect of an explosive event, the apparatus comprising:

(a) blast detection means which is arranged to detect an approaching shockwave or electromagnetic wave, caused by the explosion of an explosive device or other ordnance, and produce an output signal indicative of an explosive event, (b) a countermeasure device comprising a shaped explosive charge and a load in which the explosive charge, when detonated, causes the load to be ejected from the device as a high velocity jet at least partially in a direction towards the approaching fireball, blast-wave(s) and/or fragments, and (c) an initiator which causes the detonation of the countermeasure in response to the output signal from the blast detection means.

By combining a detection means with a countermeasure in the form of a shaped charge, it is possible to deflect or even stop incoming fragments of material associated with a blast before they impact the apparatus. Additionally the jet(s) may, by its(their) composition(s) have mitigating effects on any shock/blast wave and/or fire-ball produced by the explosive event.

The apparatus therefore provides a pre-emptive countermeasure rather than waiting for an impact to occur, as is the case with prior art explosively reactive armour.

The blast detection means may comprise a radio frequency receiver arranged to identify a signature radio frequency signal associated with an explosion. Since radio waves travel faster than the effects associated with an explosion this provides early warning of incoming effects.

Alternatively or additionally, a blast-detection means which is sensitive to other radiation, and in particular to the signature IR (Infra red) spectrum of radiation associated with an explosion of an explosive device may be provided.

Additionally a Doppler radar or other range and/or velocity detecting apparatus may be used to detect the presence and/or velocity and/or direction of motion of the fragments and/or shock wave associated with the explosive event.

The countermeasure device may comprise an open ended concave void housed within a casing, explosive charge (the ‘driver’ explosive') located around the void within the casing, and a load located within the void-space, the device being so arranged that upon detonation of the charge a detonation wave is created which causes the load to be compressed and squeezed towards the open end of the device causing the load to be ejected as a high velocity jet.

The load-containing void may be hemispherical, conical, elliptical or any other shape in cross-section. It may be of softer material than the casing, for example an aluminium liner in a stainless steel casing, or may be thinner in wall thickness than the casing. This way, the casing retains much of the explosive energy directing it into deformation of the ??liner and hence passing the energy into the load to form the jet.

The load may comprise a fluid such as water, which may contain one or more additives either in solution or suspension or both, which is retained in an optional liner by a cap across the otherwise open end of the liner. This may be, for example, a plastic or thin metal cap.

The load and the velocity of the jet should preferably be chosen such that the energy of the jet causes any incoming fragments associated with the explosion of the explosive device to be arrested, decelerated or deflected away from the apparatus.

The explosive layer may be surrounded by a ‘jacket’ of liquid (contained in a substantially rigid casing) to act as tamping for, and thus increase the efficiency of the ‘driver’ explosive's action.

The apparatus may be fitted with, or its portions constructed of, material(s) which help to mitigate the effects of the detonation of both the driver explosive and/or the explosive event on the target.

The apparatus may include more than one countermeasure device, each being initiated in response to the signal from the blast detection means.

Alternatively, more than one blast detection means may be provided with each one producing an output signal, and each of multiple initiators may be adapted to respond to selected one or ones of the output signals. This works especially well where each blast detection means is tailored to detect shockwaves whose source is located at a predetermined angle, and the countermeasures are arranged to produce jets at different angles. The countermeasure can therefore be released in the best direction to counter the blast.

A processing apparatus may be provided which may analyse the radiation detected by the blast detection devices, and may determine which of the one or more countermeasures are to be detonated to give an optimum mitigation of the incoming blast. This may include determining the timing of the detonation of one or more countermeasures in a sequenced detonation.

A typical explosive event will produce fragments travelling at a range of velocities, having a typical mean velocity of circa 1500 m/s. Any shock wave produced will typically have a velocity lower than this figure, thus at short ranges fragments tend to arrive at the target prior to the shockwave.

With a threat at 1 m distance the time to respond before the effects of the blast impinge on the target is thus 1/1500=0.000666s (667 microseconds) Commercially available (COTS) detectors for infra red radiation and for Radio Frequency (RF) radiation in the ranges associated with explosive events may have response times in the region of 10-50 and 1-10 microseconds respectively.

A COTS signal processor may have a response time in the region of 1-10 microseconds.

A COTS EBW (Exploding Bridge Wire) detonator (used to initiate the driver explosive) and its associated ‘fire set’ (driver electronics) may have a response time in the region of 1-5 microseconds.

A typical countermeasure (CM) of the type described may have a response time of around 20 microseconds.

Item Best case Worst case IR and RF Latency 50 200 IR + RF sensors 10 50 Signal processing 1 10 EBW and Fire-set 1 5 Latency CM Latency 20 20 TOTAL 81 285

The total ‘worst case’ scenario time may thus be kept below that needed to intercept the effects of a threat at a range of 1 m.

The apparatus may include means for securing the apparatus to the outside of a vehicle, such as a tank or personnel carrier or other land vehicle. Of course it could enable it to be attached to any object which would be vulnerable to attack from an explosion or other energetic event, such as a boat or aircraft, or a building or landmark.

A further application would be the provision of a barrier around an energetic device (such as, for example, an item of unexploded ordinance or an improvised explosive device IED) so that the effects of an inadvertent detonation of the device were mitigated should the device detonate.

Therefore according to a further aspect the invention provides a protective barrier for use in at least partially surrounding an item of unexploded ordinance or an improvised explosive device to mitigate the effects of an inadvertent detonation which includes an apparatus according to the first aspect of the invention. It may include a plurality of those apparatus to completely surround the unexploded ordinance or IED.

The devices of the barrier may be interconnected so that any one device that detects a shockwave or EM wave will cause the other devices to be triggered. They may all be independent, each being able to trigger independent of the others.

The barrier may include one or more protective barrier panels which can be joined to form a physical barrier to help mitigate a blast. The devices may be secured to the panels, or simply placed between the panels and the item.

The apparatus may be self contained within a housing, which may include a battery source of electrical power. Alternatively it may draw power from a remote battery located close to the apparatus. This may, for instance, comprise a battery associated with a vehicle onto which the apparatus is mounted.

The countermeasure device or devices may be fixed to the housing of the apparatus in such as manner that they can be readily replaced after they have been spent with fresh devices.

The housing may therefore include at least one opening within which the countermeasure device is received. It is useful to be able to replenish the countermeasures in the field with minimum effort required, and as such it is preferable that the detonation of the countermeasure or measures causes minimal or no damage to the functional parts of the apparatus such as the blast detection means.

According to a further aspect the invention provides a vehicle fitted with at least one of the device of the first aspect of the invention.

The vehicle may include two devices, one on each side of the vehicle. Alternatively they may be located at the front, or back, or both front and back of the vehicle. They may be located on the sides and the front or back, or the sides, front and back. They may, for instance, be secured to the sills of a vehicle below the doors, or to the front wings of a vehicle.

The vehicle may comprise an armoured vehicle such as a personnel carrier, or a tank, or other road or off road vehicle.

There now follows, by way of example only, one embodiment of the invention, described with reference to the accompanying drawings, in which:

FIG. 1 shows a vehicle with an embodiment of blast mitigating device fitted to the vehicle's sill;

FIG. 2 shows the blast mitigating device of FIG. 1 in more detail;

FIG. 3 shows a cross sectional view of a countermeasure fitted to the blast mitigation device;

FIG. 4 shows the response of the countermeasure which has been triggered by a shockwave;

FIG. 5 shows the countermeasure of FIG. 3 after it has been activated; and

FIG. 6 shows a example of a protective barrier constructed from a number of blast mitigating devices in accordance with the present invention.

FIG. 1 shows a vehicle 1 which has been fitted with an embodiment of a blast mitigating device 2 along the vehicle's sill 3. Blast mitigating devices may also be fitted to other areas of the vehicle such as: the front 4 and rear 5 bumpers; and the roof 6. The device can be positioned anywhere on the outside of the vehicle where it there is a structurally sound base for securing the countermeasures to the vehicle and where there are no other vehicle components obstructing the path of the countermeasures on deployment. In this embodiment the concern is to protect the vehicle from roadside bombs by counteracting the explosion before it reaches the vehicle substantially reducing the explosive energy imparted on the vehicle and its occupants.

The blast mitigating device of FIG. 1 is shown in more detail in FIG. 2. The device includes a blast detection means 21, a countermeasure device 22 and an initiator 23. In this embodiment all three components are included within a single casing which needs securing to the vehicle and a supply of power from the vehicle's battery. The device may be retrofitted to existing vehicles by welding the case to the vehicle's sill and running power cable from the vehicle's electric system.

The blast detection means 21 of this embodiment includes two types of sensor: a radio frequency receiver and an optical sensor. The radio frequency receiver can detected the signature radio frequency characteristics of an incoming blast wave and produces and output signal indicative that a blast is approaching. The optical sensor can detect the signature light changes associated with a blast and similarly outputs an indication signal. Since the radio frequency energy created by an explosive event is received at the vehicle prior to the full force of the explosion these sensors provide a warning signal to the initiator which triggers the release of countermeasures to counteract the blast. Sensors may be position at various locations all around the vehicle.

The initiator 23 monitors signals received from the blast detection means and when a signal is received which would indicate an approaching blast which is of a magnitude to be potentially damaging to the vehicle and its occupants, it triggers the initiation of the countermeasures 22.

An example of a countermeasure is shown in FIG. 3, in which water 31 is retained within a conical vessel 32. The vessel is surrounded by a correspondingly shaped explosive charge 33, which when detonated the conical walls of the vessel collapse inward forcing the water out of the vessel in a jet of high velocity water as shown in FIG. 5. On detecting an incoming blast the countermeasures nearest the blast are sent signals to their detonators 34 which trigger the explosion of the charge 33. The explosion blows a hole 51 in the flat end 52 of the counter measure and a high velocity jet of water 53 is expelled. The countermeasures are positioned on the vehicle so that these jets are directed away from the vehicle in the direction of the blast as shown in FIG. 5. The jet explodes into a wall of water droplets which act to dissipate energy of the approaching blast wave.

A further embodiment of the device would allow projectiles (such as rocket propelled grenades or other ordnance) to be intercepted, deflected or destroyed before they reached the target. In this embodiment the detector apparatus would be designed so as successfully to detect the signature, and/or velocity and/or direction of the approaching threat.

In a still further arrangement shown in FIG. 6 of the drawings, a protective barrier 60 is provided which can surround, preferably completely, an item of unexploded ordinance or an IED 70. The barrier comprises a number of blast mitigation devices 61-68 of the kind shown in FIG. 1 or otherwise, which are located at spaced postions around the item. They are located a few metres away from the item to allow sufficient time for them to detect a shockwave or EM wave that is produced if the item explodes, and to give time to release a counterblast wave. The devices are connected by an optional blast wall, comprising panels or ballistic armour barriers.

Each device 61-68 is positioned so that the countermeasure blast it produces when a shockwave of electromagnetic wave is detected will be directed towards the surrounded item 70. As shown there are 8 devices spaced equidistant from one another in a circle centered on the item. If the item unintentionally explodes the damage will be mitigated by the protective barrier. 

1. An explosive mitigation apparatus for use in mitigating the effect of an explosive event, the apparatus comprising: (a) blast detection means which is arranged to detect an approaching shock wave or electromagnetic wave, caused by the explosion of an explosive device or other ordnance and produce an output signal indicative of an explosive event, (b) a countermeasure device comprising a shaped explosive charge and a load in which the explosive charge, when detonated, causes the load to be ejected from the device as a high velocity jet at least partially in a direction towards the approaching fireball, blastwave(s) and/or fragments, and (c) an initiator which causes the detonation of the countermeasure in response to the output signal from the blast detection means.
 2. An explosive mitigation apparatus according to claim 1 in which the blast detection means comprises a radio frequency receiver arranged to identify a signature radio frequency signal associated with an explosion.
 3. An explosive mitigation apparatus according to claim 1 or claim 2 in which the blast detection means is sensitive to the signature IR (Infra red) spectrum of radiation associated with an explosion of an explosive device.
 4. An explosive mitigation apparatus according to any preceding claim in which the blast detection means comprises a Doppler radar or other range and/or velocity detecting apparatus which is arranged to detect the presence and/or velocity and/or direction of motion of the shock wave associated with the explosive event.
 5. An explosive mitigation apparatus according to any preceding claim in which the countermeasure device comprises an open ended concave liner housed within a substantially rigid casing, explosive charge (the ‘driver’ explosive') located around the liner within the casing, and a load located within the liner, the device being so arranged that upon detonation of the charge a detonation wave is created which causes the concave liner to be compressed and squeezed towards the open end of the liner causing the load to be ejected as a high velocity jet.
 6. An explosive mitigation apparatus according to claim 5 in which the load comprises a fluid such as water, which optionally contains one or more additives either in solution or suspension or both, which is retained in the liner by a cap across the otherwise open end of the liner.
 7. An explosive mitigation apparatus according to any preceding claim which includes more than one countermeasure device, each being initiated in response to the signal from the blast detection means.
 8. An explosive mitigation apparatus according to any preceding claim in which more than one blast detection means is provided with each one producing an output signal, and each of multiple initiators are adapted to respond to selected one or ones of the output signals, and further in which each blast detection means is tailored to detect shockwaves whose source is located at a predetermined angle, and the countermeasures are arranged to produce jets at those different angles.
 9. An explosive mitigation apparatus according to claim 7 or 8 in which a processing apparatus is provided which analyses the radiation detected by the blast detection devices, and determines which of the one or more countermeasures are to be detonated to give an optimum mitigation of the incoming blast.
 10. An apparatus according to any preceding claim which includes means for securing the apparatus to the outside of a vehicle such as a tank or personnel carrier or other land vehicle.
 11. An apparatus according to any preceding claim which is self contained within a housing, which includes a battery source of electrical power or which draws power from a remote battery located close to the apparatus.
 12. A vehicle fitted with at least one apparatus according to any of the preceding claims.
 13. A vehicle according to claim 12 which includes two explosive mitigation apparatuses, one on each side of the vehicle.
 14. A vehicle according to claim 11 or claim 12 which includes two explosive mitigation apparatuses, one located at the front and the other at the back of the vehicle.
 15. A protective barrier for use in at least partially surrounding an item of unexploded ordinance or an improvised explosive device to mitigate the effects of an inadvertent detonation which includes an apparatus according to any one of claims 1 to
 11. 16. An explosion mitigation apparatus substantially as described herein with reference to and as illustrated in the accompanying drawings.
 17. A vehicle fitted with at least one explosion mitigation device substantially as described herein with reference to and as illustrated in the accompanying drawings. 